Liquid crystal display devices are not self-emitting display devices and, therefore, almost all of them, excluding some reflection-type display devices, require a backside illuminator (so called “backlight unit”) for supplying light for display to the liquid crystal display panel. The backlight units, which are to be provided on the backside of the liquid crystal display panel (opposite to the viewer side), are generally classified into edge light type backlights and direct lighting type backlights. The edge light type is a class of backlights in which light emitted by a light source (CCFT (Cold Cathode Fluorescent Tube) or LED) placed on a side face of a light guide plate is allowed to propagate in the light guide plate and to outgo toward the liquid crystal display panel side. The direct lighting type backlights are configured such that a plurality of light sources are arranged on the back surface of a liquid crystal display panel, and light emitted by the light sources enters the liquid crystal display panel without passing through a light guide plate.
The liquid crystal display devices have a problem that the appearance of display varies depending on the viewing direction, i.e., a problem that the viewing angle characteristics degrade depending on the viewing direction. This results from the fact that the liquid crystal layer has anisotropy in refractive index so that the effective phase difference (retardation) of the liquid crystal layer varies depending on the viewing direction.
One of the known methods for improving the viewing angle characteristics of liquid crystal display devices is controlling the directivity (degree of parallelism) of light from the backlight such that rays which do not adversely affect the viewing angle characteristics are mainly allowed to enter the liquid crystal display panel and omniazimuthally diffusing the rays transmitted through the liquid crystal display panel by means of a microlens or microlens array (e.g., Patent Document 1).
[Patent Document 1] Japanese Laid-Open Patent Publication No. H9-127309
[Patent Document 2] Japanese Laid-Open Patent Publication No. 2003-50307
[Patent Document 3] Japanese Laid-Open Patent Publication No. H11-242225